July 01, 2010

Parasites and Intelligence (Eppig et al. 2010)

This is as good an explanation for global differences in IQ as I have ever seen. It proposes that IQ differences between human groups are created during ontogeny due to an energetic trade-off between brain development and immune response to infectious disease. In regions of the world with a high parasite burden, there is an elevated amount of energy used up to fight disease, at the expense of brain development.

Notice that this is not an explanation requiring genetic adaptation. Parasite burden inhibits cognitive function development. Indeed, if one were to make an adaptive argument (and I will not!), it would be in the direction of greater brain development genetic potential in parasite-heavy locales to counteract the effects of disease, i.e., the selection of individuals that may withstand the rigors of fighting off infectious disease without compromising cognitive function.

The authors write:

Multiple regression shows that, of infectious disease, temperature, evolutionary novelty and AVED, infectious disease is the best predictor of intelligence by a large margin.

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If the general pathway we propose is correct, there are two plausible mechanisms by which a trade-off in allocation of energy to immune function versus brain development and maintenance may occur. First, parasitic infection may intermittently cause the redirection of energy away from brain development. In this case, during periods of infection, the brain receives fewer energetic resources, but this allocation to brain function will return to pre-infection levels during healthy periods. During periods of infection, whatever aspects of the brain that are growing and developing will suffer reduced phenotypic quality. Second, exposure to infectious agents may cause a developmental pathway that permanently invests more energy into immune function at the expense of brain growth. In this scenario, large amounts of energy would be allocated into immune function during periods of health, as opposed to only redirecting energy during periods of infection. This could operate through a variety of mechanisms. A plausible mechanism is that higher investment in immune system is triggered by individual exposure to infectious disease at some point during ontogeny. This may include triggering from exposure to maternal antibodies while in utero.

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Our findings suggest that the heritable variation in intelligence may come from two sources: brain structure and immune system quality. Thus, two individuals may possess identical genes for brain structure, but have different IQ owing to differences in immune system quality reflecting their personal allocation of energy into brain development versus immunity.

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Our findings are consistent with a number of other findings in the literature. In particular, the Flynn effect (Flynn 1987) demands that any hypothesis regarding the worldwide variation and distribution of intelligence must be able to account for some factor that allows for large IQ gains over time spans seemingly too short to be attributed to evolution by natural selection. The parasite-stress hypothesis allows for such a factor in the form of reduced parasitic infection. As societies become modernized, decreased parasite stress may occur through multiple pathways. As national wealth increases, medicine, vaccinations and potable water can be purchased by both the government and by individuals. Moreover, there is cross-national evidence that, as democratization increases, there are corresponding increases in public health legislation and infrastructure. Democratization also increases levels of education, better allowing individuals to seek out and understand information that reduces parasitic infection (Thornhill et al. 2009). This source of endogeneity is not a flaw, but a prediction of our hypothesis.

Parasite prevalence and the worldwide distribution of cognitive ability

Christopher Eppig et al.

Abstract

In this study, we hypothesize that the worldwide distribution of cognitive ability is determined in part by variation in the intensity of infectious diseases. From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks. Using three measures of average national intelligence quotient (IQ), we found that the zero-order correlation between average IQ and parasite stress ranges from r = −0.76 to r = −0.82 (p less than 0.0001). These correlations are robust worldwide, as well as within five of six world regions. Infectious disease remains the most powerful predictor of average national IQ when temperature, distance from Africa, gross domestic product per capita and several measures of education are controlled for. These findings suggest that the Flynn effect may be caused in part by the decrease in the intensity of infectious diseases as nations develop.

27 comments:

Could be but there are many other factors such as undernourishment, violence against children and the fact that IQ tests are eurocentric in design.

Anyhow, what came to my mind as I read this at BBC this morning was that Caribbean Blacks seem to perform much better than native Afroamericans in the USA (at least on average), what strongly suggests that this is probably not the real issue because one would expect more parasite burden in the tropical Antilles than in frosty New York, right?

It seems to me that a lot of what we call intelligence has to do in fact with motivation. If your childhood entourage cheers your intellectual incursions, you are much more likely to be interested in that, regardless of genetics or whatever other biological factors, while if you are instead dismissed for that, as can typically happen in a ghetto culture of misery, then you will most likely try something else... like playing football.

Other, older studies (about 10 years) suggest that diet also influences braindevelopment. that there is a difference in average IQ between children eating fish or meat. Much fat or low fat etc.I think I can recall that lots of meat, cause high IQs. While vegetarian lifestyle causes low IQs.

I also can recall a study that claimed an influence of native tounge on brain development. Claiming that the suposedly "hard to learn" languages cause better developed brains than "Easy to learn" languages. (thats also a roughly 10 years old one)

ANd another study (20 years old) claimed, brain develops to fit the needs. And that the first 8 years of life are the important ones for brain development.That whatever tasks your brain encounteres in the first 8 years of life decides at what you will be good at.

The absoult base even should be the first 4 years of life. Hard to chew stuff in the first 4 years, cause high IQ, so the theory. Wich also backs the language theory.

Other, 20 years old numbers had been:

Chance of human beeing IQ130 (High or better: 2%

If 1 brother is IQ130+, the other (raised in same hosuehold) is in 25% of the cases also.

2 normal brothers, raised in different households did not seem to differ to 2 totaly different people.

If one oneegged twin is IQ130+, his twinbrother, raised in the same household has a 80% chance to be 130+ aswell.

Twins, raised in different households have a 50% chance of beeing both 130+, if at least one is. Wich is quiet amazing, since "normal" brothers did not seem be be connected in this case.

About 5 years ago, a Brit made european wide IQ tests (the only one I know of) wich came out like this: (map made by me)

http://img641.imageshack.us/img641/5840/durchschnittsiq.jpg

It has (more or less) central europe as top scoring one.

Its however a pretty different region. Different languages, different Y-Chromosoms. the only thing the top 3 scorers have in common is "Sauerkraut" (the top Sauerkraut eating nations are Poland, Czechia, Germany and Netherlands)

Well ok, its also roughly the Sausages area.

Ok, so you know what makes you smart:Wash your hands often! Eat Sauerkraut and Sausages and drink beer! And learn languages like Japanese, Chinese, Finnish or German. ;)

Good to see that they have some evidence that childhood disease affects brain development.

Another point that advocates for genetically based IQ difference seem to miss is that there are many in the tropics who contract a tropical disease who never get rid of the symptoms. It seems to be a common and arrogant mistake to think that a fatigued and chronically ill person will have the same IQ as a person who's life is not impacted by illness.

Not to sound confrontational, but where is the evidence that Caribbean blacks perform better than African-Americans in the United States? I've heard this factoid get bandied about, and I've also heard that it has been debunked, and that it is only true for first generation immigrants, whose children perform close to the African-American norm. I've never seen any data to support any of these three claims.

I don't understand this line of reasoning:

"if one were to make an adaptive argument (and I will not!), it would be in the direction of greater brain development genetic potential in parasite-heavy locales to counteract the effects of disease, i.e., the selection of individuals that may withstand the rigors of fighting off infectious disease without compromising cognitive function."

Ok, I understand you aren't making an adaptive argument, but I don't understand why an adaptive argument would take this form. More specifically, why would individuals who could withstand the rigors of fighting off infectious disease without compromising cognitive function be selected for, as opposed to simply individuals who could withstand the rigors of fighting off infectious diseases?

Have you read this paper by & Garrett Jones & Joel Schneider? They also discuss whether economic growth leads to improved national scores, based on the China and Middle Eastern countries it seems improvements are minimal (although they wouldn't have the same disease risks obviously).

“Considerable effort has gone into producing nonverbal IQ tests that can be used in any culture. These “culture-fair” or “culture-reduced” IQ tests have been shown to predict important life-outcomes with validity coefficients comparable to traditional IQ tests designed for specific populations…"

I have no idea where you base your belief that IQ tests are `Eurocentric`. Anyway, I will tell you smt that you might not know.

The French Foreign Legion (Legion Etrangere) is actively using IQ tests in their selection procedure, in order to weed out sub-standard candidate soldiers.

FYI, the FFA is getting lots and lots of exotic candidates, incl but not limited to, Sub-Saharan Africans, Mongolians, Chinese from all over China, SE Asians, Japanese, and so on.

I wrote `not limited to` because according to a friend of mine who`s serving in the Legion, they have had a Polynesian actually turn up at Auberne (Legion Selection Center) asking to join some years ago, or at least that`s the legend.

I have seen at least one (1) Japanese serving in the Legion, numerous Africans, and some whom I believe to be Chinese or SE Asian.

About the only nationality not seen at Auberne, is Native Australians (aka Aboriginals) I believe.

I really do not understand how a test that consists purely of Geometric shapes(i.e. shapes and geometric designs) like those FFA IQ tests, can be `Eurocentric in nature`.

Obviously, the many Africans, Asians and whatnot serving in the FFA, would probably disagree with your assessment of the IQ tests they took in order to join the Legion.

I have a feeling that you all are following the more than dubious "research" by Richard Lynn, which is a total nonsense made by a fanatic racist with racist funding out of totally disparage data.

As example, Lynn's data suggests that some peoples have average IQs of 50 or so what is extreme retardation, and would make the whole nations unable to to even survive on daily basis. This is obviously not the case: they must score badly because they are uninterested and/or do not understand what the heck is being asked of them. All that assuming Lynn has not made up the results because all his "research" stinks to pseudoscience from the beginning to the end.

The tests (and I have done some in my life, of different kinds) imply to be familiar with certain cultural categories which are not innate but learned and I imagine that in many cases they were performed in languages other than the native ones upon barely literate people.

This also applies to M, whose link soon sends the reader to Lynn's speculations, making the whole paper probably irrelevant and just another attempt of justifying racism based on pseudo-science.

The graph posted by Fanty does seem to show some (statistically insignificant in most cases anyhow) correlation between development and education quality and IQ but it probably indicates that it is development and education what favors higher average IQ scoring. All scores are within expected average: 90-110 and should oscilate somewhat in different experiments depending on the actual individuals and methods used, there's no "nation of Einsteins" anywhere.

Mark said: "and that it is only true for first generation immigrants"...

Exactly my point: they perform better because they come from a different (incidentally tropical) environment, where their skin color is not grounds for discrimination or for a particular subculture of despair.

As example, Lynn's data suggests that some peoples have average IQs of 50 or so what is extreme retardation, and would make the whole nations unable to to even survive on daily basis.

Lynn argues that Bushmen have an average IQ of about 54 which is only mild retardation and would make sense considering they are the oldest human population and suffer from malnutrion so they have both genetic and bio-environmental factors impeding their brain development. About one in 500 whites have an IQ this low or lower and such people are able to perform simple jobs and function on a basic level. As for not being able to survive, the Bushmen population is not really surviving, there are only a few tens of thousands left in the world. Also, consider other primates and early humans with IQ's WAY below 50. They were able to survive because they had other traits to compensate. Similarly, Bushmen have other traits including an incredible capacity to estimate the size of targets.

This is obviously not the case: they must score badly because they are uninterested and/or do not understand what the heck is being asked of them.

This is possible too. Bushmen are a preliterate culture and there's some evidence that never attending school can cause one to score very low on an IQ test, probably because one never develops the tendency to sit still, concentrate and focus. It's worth noting though that the IQ scores earned by individual Bushmen correlate with how intelligent other Bushmen judge them to be, suggesting that these culture-reduced tests have validity even among Bushmen.

All that assuming Lynn has not made up the results because all his "research" stinks to pseudoscience from the beginning to the end.

Actually Lynn is arguabley the best researcher of them all (certainly the most intellectually consistent). It was him who first discovered that the Flynn Effect was caused by malnutrition (including disease). The very topic of this thread was already covered by Lynn decades ago. But Lynn scares a lot of people because he's so old-school, in that he takes IQ tests at face value and considers them valid measures for just about everyone everywhere. This not only causes him to believe in huge race difference, but also to conclude that the Flynn Effect reflected a real gain in biological intelligence at a time when everyone else thought it was cultural.

This is fascinating. Somewhat related, I've always wondered, since we know viruses and bacteria can transfer genetic material to humans, if "disease load" can also affect populations in IQ due to the transfer of beneficial or harmful genetic material during infection, and be passed down.

in reference to this article http://scienceblog.com/7669/study-claims-iq-differences-at-least-50-genetic/

East Asians are the nations that score the highest, not the Europeans.

The races differ more as the tests become more g loaded (general intelligence and less culturally biased). Also the genetic-environment structure is the same each race.

Differences in the average brain size for each race are present AT BIRTH. In adulthood the average East Asian brain size (found by MRI) is one cubic inch larger than the average white, while the average white is five cubic inches larger than the average black.

When education of mother and other variables are considered you get the same results.

children tend to the average IQ of their race despite the IQ of their parents.

I'm sure that there is validity to this study. I agree that environment is an important factor but to expect a culture only explanation for the racial differences in IQ is just ridiculous.

John Ray notes that while the correlation is found in 5 out of 6 regions it doesn't occur in South America when you consider the Carribean nations.

Eppig et al say: “It is possible that local parasites … are causing these outliers”. Ray doesn't find this convincing. There is also a discussion of Dutch iq scores apparently increasing despite famine during WWII.

Europeans admire China! Even Lynn attributes them superhuman intelligence or something like that.

I don't think that's correct either. China just have certain cultural and educative patterns that fit well and even go beyond the European culture but in the same line: agnosticism, materialism, literacy, emphasis in education and exams (similar to IQ tests). Europe has only gone ahead of China these last few centuries because it was divided, and therefore autocracy could not succeed, hindering adventurism and curiosity as happened in China. When one realm applied autocracy, this damaged it and benefited another realm. In China there was always one single centralized power which could dictate laws, restricting progress. Something similar happened with the Roman Empire earlier in the West, leading to the Dark Ages.

But it's not because Chinese are innately smarter, it's a cultural, social and economical complex process, which is reflected in IQ tests possibly. There may be other factors? There might (my favorites are nutrition and social attitudes towards children and women) but need to be clearly demonstrated and I see nothing of that.

Instead I see too many abstract tests that require previous knowledge of certain cultural values which are Eurocentric indeed... and Sinocentric too. There's no test like "go to the river and read the tracks of the animals" or "how many kinds of herbs do you know?" or "play a drum"... it's certain specific kinds of "intelligence" or rather knowledge patterns which are the ones being analyzed. These patterns fit well with European and East Asian cultures but certainly not with Paleolithic or farmer societies. Civizilization and I'd dare say certain type of civilization where there are no gods that matter and no "magic" nor nature whatsoever anymore is what is being measured.

Sure, it is well known, but much less discussed, that religious belief is a factor that weights negatively in IQ scores. Makes total sense because religion is irrational and these tests are designed to measure pure rationality. But the development of this rational thought is in itself largely cultural, not biological.

John Ray notes that while the correlation is found in 5 out of 6 regions it doesn't occur in South America when you consider the Carribean nations.

Eppig et al say: “It is possible that local parasites … are causing these outliers”. Ray doesn't find this convincing. There is also a discussion of Dutch iq scores apparently increasing despite famine during WWII.

http://www.bloggernews.net/124848

The Caribbean outliers are inhabited primarily by Africans, who are not expected to have adapted to the local parasites. Most mainland south American nations, on the other hand, are inhabited by populations of substantial Amerindian heritage, and are probably expected to be better locally adapted. Indeed, the few nations where large European-descended populations exist are in the south and occupy a similar climate zone as Europe.

Maladaptation may also be one reason for African American IQ. Clearly, a simple genetic model of 80-20 European parentage predicts a much lower IQ than the observed one, thus better living conditions in the US are clearly improving African American IQ over that of their African cousins. However, African Americans live about 30 degrees of latitude north of where they evolved, and are thus expected to be maladapted to the local climate.

A second important issue is that John Ray alleges that dumb people don't make good health decisions regarding sanitation, health, etc. and causation runs the opposite way.

That makes no sense, as good sanitation practices has existed on and off in the western world since antiquity, and were institutionalized in a scientific manner in the modern age. Roman-era Europeans used baths, a practice largely abandoned in the Middle Ages.

Moreover, parasite load is objectively higher in the tropics than in more northern latitudes, even for non-human species, which obviously don't have any sanitation decisions to make.

"The Caribbean outliers are inhabited primarily by Africans, who are not expected to have adapted to the local parasites."

You said before that the article makes an argument that does not require genetics. Here you seem to introduce genetics into the equation.

Since Africa-Carribs have lived for generations in the Caribbean you must be saying that their genes do not produce phenotypes suited to the local parasites as the natives do. If that is your argument, that populations have different immune systems due to genetic evolution, then it would likely be the case that some populations have stronger immune systems due to the same evolution process. And because of the trade off between immune system and brain development the result is a less intelligent population by genetics.

Most people do not argue a genetic only argument, nor would I. It should be noted that mixed populations have an IQ in between each of their parent populations. The reason for this is certainly in part due to genetics considering the fact that races differ most significantly on the g-loaded tests and score the same way after controlling the mothers education and other cultural factors. I don't know if the mixed Africans who's IQ was measured really are 80% black and 20% white (that might only be the average African American and not representative of the mixed Africans studied). In either case I have no reason to expect the African Americans to have an IQ of (100)(.2)+(70)(.8) since their are also environmental factors and why would you expect heritable IQ to follow such simple math anyways.

Another point is that surely the more intelligent populations are more likely to have greater sanitary practices, which serves to strengthen the correlation between parasitic threat and lower intelligence.

You do realise that even when populations move their IQ is basically the same. Also notice that some of the smartest populations in the world live in the tropics; they include the Taiwanese and people of Singapore who are largely descended from immigrant Chinese.

Lastly the Southeast Asians and tropical native Americans have a much higher IQ than pure sub-saharan Africans. This is not consistent with environment/acquired immune system. Instead it is more consistent with out of Africa colder climate genetic adaptation.

You said before that the article makes an argument that does not require genetics. Here you seem to introduce genetics into the equation.

I said that their argument did not require selection, not that it did not require genetics.

A population subject to a particular pathogen will acquire some resistance to the pathogen with natural selection. Selection, however, selects for the individuals that survive, that does not mean that the individuals (as individuals) will thrive.

For example, many populations in Africa have adapted genetically to malaria. That does not mean that they don't get sick, weak, and suffer during malaria bouts, only that they survive the disease. The disease still takes a toil on their body.

The argument the authors make is that different populations experience different parasite loads, and thus get "sick", at different rates, with people inhabiting parasite-heavy areas being particularly disadvantaged.

Imagine a cluster of houses built to withstand wind erosion, and another built to withstand saltwater erosion. Both of them are "adapted" to their local environments, yet both are battered by their local environments. If you built a salt-resistant house in the windy plains or, conversely, a wind-resistant house by the shore, then it'll get ruined faster.

The fact that people adapted to African climate, diet, flora and fauna were transplanted to a different continent, with a different climate, and started consuming a different diet, does seem like a very negative thing for their development.

Another point is that surely the more intelligent populations are more likely to have greater sanitary practices, which serves to strengthen the correlation between parasitic threat and lower intelligence.

As I said above, good sanitation practices are a recent invention. Besides, increased parasite load in the tropics is objective. Cut your finger in the arctic or in the jungle, and guess which one is more likely to get infected, no matter what your "sanitation practices" are.

Also notice that some of the smartest populations in the world live in the tropics; they include the Taiwanese and people of Singapore who are largely descended from immigrant Chinese.

These are modernized populations, which enjoy good healthcare and sanitation. Was the rice-eating small-scale farmer from China who didn't have access to Western medicine as intelligent as the modern Chinese from the cities, or was he more similar to people living in poverty elsewhere in the world today?

"Our findings suggest that the heritable variation in intelligence may come from two sources: brain structure and immune system quality. Thus, two individuals may possess identical genes for brain structure, but have different IQ owing to differences in immune system quality reflecting their personal allocation of energy into brain development versus immunity." -from article

Races differ most on the g-loaded parts of the test and the genetic part (discovered by twin studies I think). Importantly the races also have the same gene-environment architecture.

For a culture/envirronment only explanation there would have to be an environmental/cultural factor that only effects people between races but not within races and it would have to have a consistent and greater impact than all the other cultural factors. And this would have to be true for every race. That would be ridiculous to say.

In this context individuals within a race do differ in their immunities and their parasitic load.

Also populations that move basically keep the same IQ(of course changed a bit by cultural and environmental change)

Kids of interracial relationships have intermediate iqs (albeit not perfectly average) and the IQ of childreen tend towards the average IQ of their race. Both can't be explained by culture/environment alone.

"Besides, increased parasite load in the tropics is objective. Cut your finger in the arctic or in the jungle, and guess which one is more likely to get infected, no matter what your "sanitation practices" are."

Once again, why are some of the smartest populations in the world located in the tropics. The people of Singapore and Taiwan, largely descendants of Chinese immigrants, have very high IQ. Their "parasitic load" has increased objectivity yet they still boast an IQ higher than nearly all populations, both in and out of the tropics.

More to the point why are SE Asians and tropic living native Americansat at significantly higher IQs than subsaharan blacks? (That could be explained in part by out of Africa cold climate adaptation.)

Lastly to answer your question the poor Chinese Guy would be smarter than the poor Indian or the poor black Guy in Africa.

The people of Singapore and Taiwan, largely descendants of Chinese immigrants, have very high IQ. Their "parasitic load" has increased objectivity yet they still boast an IQ higher than nearly all populations, both in and out of the tropics.

Parasite load is a major problem in the absence of good sanitation practices. Someone who lives in a western-style home in Bengal is not exposed to the same parasite load as someone who toils in the field or lives in the slums. Singapore is a city-state with very high standards of living, it's not the wild.

"Parasite load is a major problem in the absence of good sanitation practices. Someone who lives in a western-style home in Bengal is not exposed to the same parasite load as someone who toils in the field or lives in the slums. Singapore is a city-state with very high standards of living, it's not the wild."

I agree that it could be a factor in explaining the variability of racial iqs but only a small one. And I go further to make the point that culture and environment aline cannot explain racial IQ differences.

Remember that living standards goes both ways; better living conditions can help IQ w but higher IQ leads to better living conditions too.

Remember that living standards goes both ways; better living conditions can help IQ w but higher IQ leads to better living conditions too.

99.999% of people enjoy good living conditions not because of any high IQ of their own, but because of a handful of individuals who invented stuff. The population average IQ has nothing to do with it; if it did, then most of these inventions would've come from East Asia which has more people and higher IQ, but this is not what we actually observe.

For example, most people in the first world take for granted that their tap water is not polluted (or even drink bottled water), and that they can go to the doctor if the get infected. That is not the case in most of the rest of the world. It's not a matter of IQ, as most people in the first world didn't have these luxuries themselves a few generations ago. It is rather a matter of cultural hysteresis caused by bad governance, limited resources, ethno-religious strife and the like.

"99.999% of people enjoy good living conditions not because of any high IQ of their own, but because of a handful of individuals who invented stuff. The population average IQ has nothing to do with it; if it did, then most of these inventions would've come from East Asia which has more people and higher IQ, but this is not what we actually observe."

Cmon... having higher iqs makes you more productive, both as individuals and as populations. There is a correlation between the IQ of a nation and its gdp. There is even a correlation between the national IQ and Nobel prizes. That correlation exists globally and exists within Europe, Asia, and Africa.

Those things aren't disputed, both the differences in IQ and a relation of IQ and economic status of a population. The only question is whether genetics is causing the differences in the IQs. I have already shown that to be the case: Wednesday, October 20, 2010 11:35:00 PM

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